Access control systems are used extensively in security systems to ensure that only authorized people gain access to secure areas. Tailgating refers to the situation where one or more unauthorized people follow an authorized person through a secure portal such as a doorway or turnstile. Tailgate detection systems using infra-red beams have been used in optical turnstiles and in doorway tailgate detection systems for some time.
Early systems such as the prior art system of FIG. 1 use a small number of beams (sometimes only one) and are time based. Using the system of FIG. 1 as an example, the beams run perpendicular between pedestals 101 and 102. This means that when access is given, the beams are shunted or ignored for a fixed length of time to allow an authorized person 103 to pass through. If the beam(s) is broken at any other time, an alarm is generated. The shunt time has to be long enough for person 103 to pass completely through including trailing arms and legs. The problem with these systems is that two or more people, such as tailgater 104, can quickly pass through in the time allowed for the slower people to pass through. These systems also do not detect the direction of travel.
Later systems added more beams. Initially only perpendicular beams then some systems included diagonal beams. These systems now rely on patterns of beam breakages instead of time. They are able to identify direction of travel. The first systems detected tailgaters a couple of inches behind the authorized user. The current standard is now ¼″.
The problem, particularly with wider passageways, is that tailgaters are not always directly behind the authorized person. They can be partially or even completely overlapped. FIG. 2 shows a situation where the authorized person 203 and tailgater 204 are partially overlapped in the passageway between pedestals 201 and 202. FIG. 3 shows the situation where the authorized person 303 and tailgater 304 are completely overlapped in the passageway between pedestals 301 and 302. The scenarios shown in FIGS. 2 and 3 are referred to as “overlap tailgating” or “overlapped passage.”
Therefore, in secure portals with wider passageways, prior art tailgate detection systems fail to detect tailgaters who either partially or completely overlap with an authorized person. This could lead to serious security breaches. There exists a need for tailgate detection systems which are able to detect overlapping tailgaters in wider passageways.